This invention concerns a noise preventive equipment for an endoscope which makes it possible to display a true and clear image of a subject on the display unit while preventing the high-frequency current from the cauterizing power circuit used to drive high frequency incision and excision tools from giving noise to the picture signal obtained by the solid state pickup element when the endoscope using a solid state pickup element is used together with high frequency incision and excision tools.
Conventionally used medical endoscopes consist of a hard type endoscope with a hard and semi-linear inserting member and a soft type endoscope with a soft inserting member which can be inserted into a human body through the mouth. These endoscopes have an image forming optical system consisting of an objective lens which observes inside of the body and forms an image, at the end of the inserting member. With this image forming optical system which sends the formed inside image to the end of the image guide on the operating unit end through the channel of an optical fiber bundle called an image guide, the image inside the subject can be observed through the eye lens. From the operating unit, illuminating light from the light source equipment is irradiated to the subject through a light guide cable consisting of the same optical fiber bundle. Furthermore, the inserting member of the endoscope has a channel to introduce therethrough a forceps, high-frequency scalpel, etc. from the operating unit to the end of the inserting member so that the medical treatment and biopsy can be performed while observing with the endoscope.
Owing to the recent progress of electronics, such solid state pickup elements as a CCD (Charge Coupled Device), a BBD (Bucket Brigade Device) and a MOS type sensor which can capture the image as an electrical signal have been developed, and these solid state pickup elements are being used at the end of the inserting member of the endoscope.
But when the high-frequency cauterization and excision surgery and biopsy are conducted with an endoscope using such a solid state pickup element and high-frequency incision and excision tools (hereinafter called high-frequency scalpel), the high-frequency current from the cauterizing power source for the high-frequency scalpels is read by the scanning solid state pickup element and superimposed as noise on the picture signal, thus making the picture displayed on the display unit indistinct.
The frequency of the high-frequency current generated by the high-frequency scalpel is set to a value which does not affect the human body. The proper frequency is usually higher than 300 (KHz). On the other hand, the color picture signal has the frequency band of, for example, 4.3 (MHz). Therefore, the frequency band of the high-frequency current overlaps the lower band of the picture signal.
FIG. 1 is a spectrum map to show this relationship, with the axis of ordinates showing spectrum strength and axis of abscissas showing frequency, and N represents the spectrum of the color picture signal and H the spectrum of high-frequency current. When the band of the high-frequency current overlaps that of the picture signal like this, the picture displayed on the display unit becomes indistinct and what is worse, the operation must be stopped. As a measure to solve this problem, the patent application No. 69530/83 and No. 69528/83 issued by the Patent Office in Japan proposed that the portion where the high-frequency current runs be shielded and the frequency of the high-frequency current be raised to avoid the band of the frequency picture signal and the frequency of the picture signal be raised to avoid the frequency band of the high-frequency current, but both of them are not able to remove positively the high-frequency current, the cause for the noise, from the picture signal.